A camshaft adjuster of this type is the subject of DE-C-34 21 028 and corresponding U.S. Pat. No. 4,716,864. These documents describe two different camshaft adjusters, both of which are mounted between the two strands of a chain. In the first camshaft adjuster, one tensioning shoe is rigidly attached to the housing. The opposing tensioning shoe can be moved a certain distance out of a cylinder by means of a piston by applying pressure to a pressure chamber, so that its distance from the fixed tensioning shoe can change and thus cause a change in the chain tension. Allegedly, adjustment of the valve timing also is possible by changing the chain tension.
In the second embodiment of a camshaft adjuster described in DE-C 34 21 028 both tensioning shoes are connected to a single piston, so that both tensioning shoes always move the same distance in one direction. In this way the chain tension, if any, remains unchanged, but the timing of the driven camshaft can be changed by shortening one strand of the chain and lengthening the other strand by the same amount. However, maintenance of a prescribed chain tension is important for the life of chain drives and for low-noise operation, so it is desirable to provide a tensioning mechanism in addition to the described camshaft adjuster, but there is no provision for this in the cited document. In many cases, however, there is no room for such a tensioning device, especially between the strands of the chain, if the camshaft adjuster is already located there.